Gyroscope monitoring alarm system



A ril 18, 1961 1. LUIK 2,980,895

GYROSCOPE MONITORING ALARM SYSTEM Filed Dec. 22, 1958 IN V EN TOR.

i4 M4! 4 01A 'GYROSCOPE MONITORING ALARM SYSTEM Ilmar Luik, CedarRapids, Iowa, assignor to Collins Radio Company, Cedar Rapids, Iowa, acorporation of Iowa Filed Dec. 22, 1958, Ser. No. 782,646

3 Claims. (Cl. 340-413) This invention relates to monitoring alarmsystems for gyroscopes such as used in navigational systems to indicatethat an erection means has failed to maintain the spin axis of thegyroscope in a predetermined attitude. This alarm system provides morethorough monitoring than that provided by previous systems and hasasimple flag indicator that may be a part of the usual type ofnavigational display instruments.-

An object of this invention is to provide a monitoring system thatactuates an alarm device within a predetermined interval after theerection means of a navigational system fails.

Anotherobject is to provide a positive operating simple alarm indicatorthat operates in response to actuation of the usual switches forcontrolling erection motors of the gyroscope.

A feature of the invention provides instant alarm indication in responseto interruption of voltage that is also applied to the attitude sensingelements of the gyroscope.

In the system shown in the accompanying figure, two individual delaycontrol circuits are coupled to corresponding erection motor controlcircuits that are associated with the two difierent mounting axes of thegyroscope gimbal. Each delay control circuit includes a capacitor thatis normally charged when the motor control switches are in a positionthat is normal in response to the spin axis of the gyroscope being in adesired attitude. When the spin axis departs from the desired attitude,one or both of the erectionmotors normally operate immediately to returnthe spin axis to its proper attitude. During the interval that isusually required for returning the spin axis, a charging voltage isremoved from that capacitor which is in that delay circuit correspondingto the motor which is in operation. Upon removal of the chargingvoltage, the capacitor commences to discharge through an input circuitof a current control circuit of the alarm indicator. The alarmindication is delayed by the discharge current from the capacitor sothat normally there is sufficient time for the erection motor to returnthe spin axis to its normal attitude and thereby prevent operation ofthe alarm indicator. Should there be a malfunctioning of the erectioncircuit so that the return of the spin axis is delayed more than thatinterval required for discharging one of the capacitors, a red flag orother alarm indicator is operated.

The flag being used as an alarm indicator is constantly scope is mountedin the usual gimbal that has trunnions 2,980,895 Patented Apr. 18, 1 9614 and 5 on axes that are perpendicular to each other and perpendicularto the spin axis 3. The spin axis 3 is maintained in a vertical positionby operation of erection motors 6 and 7. Erection motor 7 is effectivein applying torque between the inner ring 8 of the gimbal and trunnion 4and likewise, erection motor 6 is efiective in applying required torquebetween the outer ring 9 of the gimbal and the trunnion 5. The erectionmotors are the alternating-current capacity type that lack torque whenthe current through two portions of the motor windings are equal butprovide torque when the current through the two portions of the motorwindings are unequal, the direction of the torque being reversed as thegreater current flow is transferred from one portion of the windin tothe other.

Current for torque motor 6 is controlled by gravityoperated mercuryswitches 10 and 11 that are mechanically coupled to trunnion 4 andlikewise current for torque motor 7 is controlled by gravity-operatedmercury switches 12 and 13 that are coupled to trunnion 5. When spinaxis 3 is vertical, the switches are closed, but when the spin axis istilted with respect to either mounting axis by more than 5 degrees fromvertical, one of the switches mounted about that axis is opened. Thedirection of the tilt about the axis determines which switch is opened;the other switch on the same axis is opened in response to a tiltgreater than 5 degrees in the opposite direction. The operation ofgravity switches for controlling a torque motor is described in U.S.Patent 2,474,549 entitled Gyroscope, issued to John F. Schoeppel on June28, 1949.

Each of the switches shown in the accompanying figure have two contactsthat are individually closed to a common contact in response todifferent degrees of tilt of the switch. For example, in switch 10common contact '14 is normally connected through mercury globule 15 tocontact 16 when the switch is in a normal position for indicating avertical position; the common contact is connected to contact 17 inresponse to a tilt of 2.5 degrees from its normal position; and theswitch is completely open in response to a tilt greater than 5 degrees.The erection motors operate at one rate for a tilt greater than 5degrees andat a slower rate for a tilt less than 2.5 degrees.

The alarm circuit of the present invention has delay control circuits 18and 19 connectedindividually to the pairs of switches for controllingerection motors 6 and 7 respectively. With reference to that circuitconnected to erection motor 6, primary windings of step-up transformers20 and 21 are connected between ground and switches 10 and 11respectively. When the spin axis is in a normal vertical attitude withreference to trunnions 5, current flows from source 47 ofalternating-current through parallel circuits comprising two portions ofthe winding of erection motor 6 through closed switches 10 and 11 andprimary windings of transformers 2t and 21 respectively. The secondarywindings of transformers 20 and'21 are connected in series so that thevoltages induced into the secondary windings from the primary windingsare added and applied across a delay control circuit 23. The delaycontrol circuit comprises electron discharge device 24 connected inseries with a diode rectifier 25 and capacitor 26. A discharge circuitconnected assuage axis a of rotor 2 is in a normal vertical attitudewith respect to trunnion 4, current flows from source 48 throughparallel windings of motor 7 for applying maximum voltage to capacitor44.

In response to departure of the spin axis from vertical relativetotrunnion 5, the voltage that is induced into the serially connectedsecondary windings of transformers 2t and 21 is reduced below that pointrequired for maintaining discharge tube24 conductive and, therefore,capacitor 26 commences to discharge through primary winding 27 ofsaturable inductor 28, the winding of saturable choke coil 30, andresistor 31. Aslong as substantial discharge current flows through theprimary winding 27, the impedance of the secondary winding 29 of"saturable reactor 28 is sufiiciently, low to maintain the requiredcurrent flow necessary to retain the alarm indicator in a condition thatindicates normal operation. Ordinarily the spin axis 3 of gyroscoperotor 2 will be returned to its vertical position by operation oferection a motor 6 before capacitor 25 is sufiiciently discharged tocause an alarm indication.

It is evident that in the event the. erection motor is unoperative, and,therefore, unable to. return the spin axis to its vertical position,capacitor 26 will become discharged to the point that the current flowthrough winding 27' of reactor 28 is insutficient to saturate the coreof the reactor. Therefore, the impedance of secondary winding 29increases sufficiently to greatly reduce the current fiow to theoperating circuit of the alarm indicator. The alarm indicator respondsto the substantial reduction of current to indicate failure. Should aconnection in the operating circuit of the erection motor 6 become openor should the Winding itself of the motor become open, capacitor 26 willdischarge to cause a failure indication even though spin axis 3 isvertical.

The operating circuit of the flag alarm includes terminal 32 that isconnected to a source of alternating current, secondary winding 29 ofsaturable reactor 28 that is connected for monitoring the operation oferection motor 6, secondary winding 33 of saturable reactor 34 that isconnected to the circuit for monitoringerection motor 7, full waverectifier 35, and relay winding 36. Normally the voltage, acrosscapacitor 26 of delay control circuit 18 and the corresponding capacitor44 of delay control circuit 19 is suflicient to maintain the cores ofreactors 28 and 34 saturated. The total impedance of serially connectedwindings 29 and 33 of the saturated reactors is low to allow sufficientalternating-current flow to rectifier 35 for maintaining the requireddirectcurrent flow from the output of the rectifier to hold relay 36operated. The operating circuit for energizing the winding of solenoid40 to retain alarm flag 41 in a normal position may be traced fromterminal 45 that is connected to a source oi direct-current voltage,through limit switch contacts 3% that are normally closed in response tothe rotor of gyroscope ll being uncaged, limiting resistor 39, contacts3-7 of relay 3'6, and through winding 40 to ground. 7

When either capacitor 26 or 44 have discharged below a certain point,the impedance of the respective saturable reactor load winding 29 or 33increases substantially and thereby causes sufiicient reduction incurrent flow through solenoid winding 40 to allow flag 41 to be operatedeither by force from a spring or by gravity to that position forindicating alarm. Since the removal of voltage from terminal 32 causesan immediate alarm signal, this voltage is constantly monitoredand'indicates that normal voltage is available to any circuits that areconnected to this same source; for example, synchro rotors 42 and 43that may be coupled to gyroscope 1 for indicating the attitude of thegyroscope mounting base relative to the vertical spin axis 3.

Specifically, with regard to one model of an automatic pilot foraircraft navigation, the discharge device 24 is a neon glow tube thationizes in response to the application of approximately 60alternating-current volts to the delay control circuit. Transformers 20and 2-1 have the proper step-up ratio for applying approximatelyalternating-current volts to the delay control circuit 23 in response tothe erection motor 6 being connected directly to the transformersthrough closed gravity-operated mercury switches 10 and 11. When eitherof these switches is open, the alternating-current voltage that isapplied to the delay control circuit drops to 40 volts and tube 24becomes nonconductive. The capacitor 26 as well as the correspondingcapacitor 44 has a capacitance of .80 microfarads and discharges througha circuit that includes resistor 31 which has a resistance of 100,000ohms. These values provide sufficient current during an interval fourtimes as long as the time constant of the discharge circuit formaintaining sufficiently low impedance across the secondary windings ofreactors 28 and 34 to maintain the flag alarm in 'a normal position.Resistor 46 that is shown connected to contact 17 of gravity-operatedmercury switch 10 completes a circuit for the erection motor when thespin axis 3 is Within about 2.5 degrees of vertical and causes theerection motor to operate at a slower speed than at that speed at whichit operated when the switch 10 is completely open. While the operatingcircuit is being completed through resistor 46, the voltage that isapplied to delay control circuit 23 is sufficient for ionizing dischargetube 24 so as to prevent an alarm indication.

Although this invention has been described with respect to a particularembodiment shown in the accompanying figure, the alarm circuit may bemodified in ways obvious to those skilled in the art and still be withinthe spirit and scope of the following claims.

What is claimed is:

l. A failure alarm for a gyroscope, said gyroscope being of the typehaving a rotor with a spin axis oriented in a predetermined attitude, aplurality of electrical switches, an erection motor, each of saidswitches being connected in series in an operating circuit for saidmotor, different ones of said switches being operable from a normalclosed position in response to departure of said spin axis in differentdirections about an axis of said rotor tov open said respectiveoperating circuit, said failure alarm comprising an alarm signalingdevice, a capacitor,

eans responsive to all of said operating circuits of said :motor beingnormally closed for applying across said capacitor direct-ctu'rentvoltage higher than a first predetermined voltage, means responsive toany of said motor operating circuits being opened for removing saiddirect-current voltage in order to allow discharge of said capacitor,said signaling device being disabled for indicating alarm by thepresence across said capacitor of voltage higher than a secondpredetermined voltage which is lower than said first predeterminedvoltage, said signaling device after an interval that is determined bythe discharge rate of said capacitor operating to indicate faultyoperation of said gyroscope, and said signaling device continuing to bedisabled to prevent an alarm indication in response to all of saidoperating circuits being normally completed during said interval.

2..A failure alarm for a gyroscope comprising, a pair of erectioncurrent control circuits including transformer means, each of saiderection current control circuits conducting normal current in responseto the spin axis of said gyroscope having a predetermined attitude, analarm control circuit including a discharge tube, a rectifier and acapacitor connected in series,tsaid discharge tube becoming conductivein response to the application of voltage higher than a firstpredetermined voltage across said alarm control circuit,said-transformer means in response to the normal flow of current in eachof said erection current control circuits applying voltage higher thansaid first predetermined voltage across said alarm control circuit forcharging said capacitor, an alarm signaling device menses connected tothe output of said capacitor, said signaling device providing a normalindication in response to the voltage across said capacitor beinggreater than a second predetermined voltage which is lower than saidfirst predetermined voltage, said discharge tube becoming nonconductivein response to the departure of said spin axis from said predeterminedattitude to disconnect said capacitor from said transformer means fordischarging said capacitor at said discharge rate, said signaling devicebeing operated to give an alarm indication in response to the voltageacross said capacitor becoming less than said second predeterminedvoltage Within an interval determined by said discharge rate, and saidsignaling device being retained unoperated to prevent an alarmindication in response to the spin axis of said gyroscope being returnedto its predetermined attitude within said interval.

3. A failure alarm for a gyroscope, said gyroscope being of the typehaving a rotor with a spin axis oriented in a predetermined attitude,said rotor being mounted for allowing rotation of said spin axis aboutfirst and second perpendicular mounting axes, first and second torquemotors operable for rotating said rotor about said first and secondmounting axes respectively, first and secnd pairs of switches forcontrolling operation of said first and second motors and operable inresponse to rotation of said spin axis about said first and secondmounting axes respectively, said switches normally being closed,difierent ones of said switches being opened in response to rotation ofsaid spin axis'in different directions from said predetermined attitudeabout respective ones of said axis; said failure alarm comprising firstand second transformers having primary windings connected through saidfirst and second pairs of switches to said first and second motorsrespectively, first and second delay control circuits connected acrossindividual secondary windings of said first and second transformersrespectively, each of said delay control circuits having a dischargetube, a rectifier and a capacitor serially connected, each of saiddischarge tubes becoming conductive in response to the application ofvoltage higher than a first predetermined 6 i voltage to said alarmcontrol circuit, means for applying through each of said transformersand a respective pair of said switches voltage higher than said firstpredetermined voltage to the respective one of said discharge tubes inresponse to the respective pair of said switches being normally closed,each of said capacitors becoming charged to said higher voltage inresponse to the respective one of said discharge tubes becomingconductive, a saturable reactor and a resistor for each of said delaycontrol circuits, each saturable reactor having a control winding and aload Winding, said control winding and said resistor for each delaycontrol circuit being connected in series to form a discharge circuitacross the respective one of said capacitors, a source of alternatingcurrent, an alarm signaling device, said source of altermating-current,each of said load windings, and the input circuit of said alarmsignaling device being connected in series, the impedance of said loadwindings normally being of such low value that sutficient current flowsthrough said input circuit to maintain said signaling device in anonalarm state, said discharge tube for either delay control circuitbecoming non-conductive in response to one of said switches that isconnected through a respective one of said transformers to a respectivedelay control circuit being opened by departure of said spin axis fromsaid predetermined attitude to start discharging of a respectivecapacitor at a rate determined by the resistance of said dischargecircuit, the impedance of the load winding of said saturable transformerthat is connected to said discharging capacitor increasing in responseto the decreasing discharge current to operate said signaling alarmdevice within a predetermined interval after the respective one of saiddischarge tubes becomes nonconductive, and said signaling alarm devicebeing retained in it nonalarm state providing the spin axis of saidgyroscope is returned to its predetermined attitude within saidinterval.

Letfier May 6, 1956 Warner Apr. 15, 1958

